The Philosophy of SPC
The
Elevator
Pitch!
Traditional Product-oriented Quality Control programs emphasize defect detection, relying heavily on inspection, scrap, and rework. In other words, it pays workers to make defects and then to correct them.
The goal of SPC is defect prevention, through improving the production system.
How deep does
the rabbit hole go?
Most companies start out using SPC with the objective of ensuring that the production process is stable and capable of producing products to the specification. But this is just touching the surface of what is possible with a robust SPC program, and as these initial objectives are met, the program should shift to improving the system.
The usual course of progression for companies trying to implement SPC programs is,
- Monitor variation and take necessary preventative measures before more value is added.
- Eventually you understand that variation is unavoidable in manufactured products. Further, a distinction is made between common cause and special/assignable cause variations.
- For continued growth, companies start creating control process flow charts and Pareto charts. This gives the company a better insight into their manufacturing process, while also identifying the most significant causes of quality problems.
- Once the efficacy of SPC has been established in multiple small result-centered programs, SPC is accepted as the standard way of doing things and becomes an expectation for vendors to implement as well.
I’m in, but
How do I
implement SPC
for a project?
Generally, when starting out with implementing SPC, the following course of action is recommended,
Step 1. Target one project for quality improvement
For the biggest “Bang for the buck”, choose the most frequent and costly quality problem. Usually identified through customer claims and a Pareto analysis.
* Too often companies fall into one of the following two traps when trying to implement SPC,
-
Making SPC the sole responsibility of the quality department
Without the proper understanding of the theory behind SPC, and due to the lack of evidence specific to their company, management and production personnel are often resistant to any changes suggested, thus making a return to old ways inevitable.
-
Large-scale, activity-centered programs
Some companies commit whole-heartedly to SPC and start enforcing strict guidelines for the various production processes. This is an activity-centric approach which isn’t driven by the positive results that SPC can help produce. These attempts rarely lead to success, but often flounder and die due to lack of results. Leaving the company cynical of all quality improvement techniques.
Step 2. Determine where the problem is and what is causing it
Use flow charts for the manufacturing process, in order to come to a consensus about the actual steps involved in the process, versus the ideal. Once established, use the flow charts to develop a list of possible causes for the problem and determine the root cause using cause-effect-analysis.
Step 3. Determine the current status of the process
Using common SPC tools such as Histograms, control charts, and process capability analysis, find out the following the characteristics of the process,
- Where is the process centered?
- What is the spread around the center?
- Is the process stable and predictable?
- What is the defect rate?
Step 4. Take action to solve the problem
Based on the information gathered in the previous steps and a solid understanding of SPC, determine the specific steps to solve the problem.
These steps might involve,
- Re-centering the process
- Searching for and eliminating sporadic problems
- Minimizing operator overcontrol, by instructing them to make adjustments only when a control chart indicates that adjustments are needed
- Looking for ways to reduce the natural variability of the process
Once the project is completed, make sure to write a concise final report. This report should state the problem being addressed and its root cause, the status of the process before the project began (including things like defect rate and production efficiency), the actions taken to address the problem, and the status of the project at the end of the project, and finally, it should include an estimate of the monetary impact to the company. Optionally in order to assist with future projects, also try to document the steps taken and whether a step was helpful or not.
Concluding thoughts
…
Where to go from here?
Familiarity is the key value provided by a robust SPC program. Familiarity not only with your own processes but also the capabilities of your suppliers. It brings Objectivity in place of subjective opinions and estimates. Having numbers to quantify results inspires Confidence and establishes a sound basis to Evaluate the most pressing needs, and the Analyze the cost to address those concerns.
At a more primary level SPC programs often lead to a much Deeper Understanding of the manufacturing process, its present Limitations and the Feasibility of the specification its targeting. Before you even gain any meaningful insights, the process of implementing an SPC program should serve as a deterrent to Reckless Spending in pursuits of solutions that won’t work, in order to solve a problem that may not exist.
When done right, targeting Single Projects at a time, it’s easy to integrate and the results-based approach makes the changes more palatable for management and production personnel. It serves as a Safety Net for everyone involved by ensuring that resources are being used optimally and the highest levels of quality are being achieved. Gradually you find that SPC has a positive impact on every aspect of production, with the decrease in defects, a better sense of the process and Sense of Ownership of the product there is marked boost to Employee Morale.
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